This invention is in the field of surgery, and more particularly, arthroscopic surgery on joints such as knees, shoulders, or hips. It relates to using arthroscopic devices and methods to replace damaged or diseased cartilage surfaces in mammalian patients.
Cartilage is the type of tissue that coats the ends (or other friction-bearing sites) of various types of bones. It is reasonably hard but not rigid. In a healthy joint, cartilage is characterized by a smooth, slidable surface, to promote comfortable and unhindered movement of the joint; however, in a damaged or diseased joint, the cartilage on one or more bone surfaces may need to be repaired or replaced.
Because of various load-bearing and other physiological factors, the joints that most frequently need surgical repair or replacement are knee joints, hip joints, and shoulder joints; however, other joints (such as finger joints, ankles, etc.) also occasionally need repair, due to injuries, arthritis, and other problems.
To describe and illustrate this invention, the discussion below focuses mainly on knee joints. The initial discussion, which describes and illustrates a relatively simple and basic form of the invention with few enhancements, focuses on a femoral-tibial compartment, i.e., the main load-bearing surfaces between the femur (the thighbone) and the tibia (the shinbone). After that description, various enhancements to this invention are described and illustrated in a patello-femoral interface, since it is easier and clearer to illustrate that simpler part of the knee. However, it should be recognized that the various positioning, anchoring, and other enhancements that are described and illustrated with respect to the patella (the kneecap) can also be adapted if desired to replacing a damaged cartilage segment in a femoral-tibial compartment as well.
In addition, it should be kept in mind that the methods and devices disclosed herein also can be used to repair other types of joints, including shoulder and hip joints. Indeed, because the condyles (i.e., the rounded surface at the end of a bone) in knee joints have complex shapes that are more difficult to work with than the simpler ball-and-socket joints in shoulders or hips, development of this invention to repair complex and difficult knee joints clearly indicates that this invention can be adapted to the simpler joints found in shoulders, hips, and elsewhere.
Various "classical" techniques, tools, and implanted devices that have been used for many years to repair damaged cartilage in knee joints are discussed in medical texts such as Campbell's Operative Orthopedics, a five-volume treatise.
Other recent developments, most of which focus on ways of transplanting chondrocyte cells (which generate cartilage) from healthy cartilage into damaged cartilage areas, are described in various articles such as Brittberg 1994, Minas et al 1997, Thornhill 1997, and Chen 1997.
U.S. patents that disclose various types of surgical tools and implantable devices for repairing knee joints can generally be classified into two categories (although, as noted below, these categories have begun to overlap substantially in recent years). The first category, which generally includes older patents, is limited to surgery which requires that the knee must be cut open, to expose at least a portion of the bones that are being worked on, giving the surgeon direct access to the areas being worked on. This type of operation is used in various situations, including: (1) patellar implants, in which a device is inserted to assist a damaged patella (kneecap), as described in U.S. Pat. No. 3,927,423 (Swanson 1975); and, (2) cases that require what surgeons call a "knee replacement" or "total knee replacement" (abbreviated as TKR), in which the ends of the tibia (shinbone) and/or the femur (thighbone) are either cut off or otherwise cut, grinded, or machined to prepare an exposed bone surface, followed by permanently implanting one or more devices on the exposed bone surfaces. Currently, the only TKR devices that have been approved for use in the United States use a metal-surfaced femoral component and a plastic-surfaced tibial component. However, other interfaces have been developed for other joints (including metal-on-metal devices for use in the hip), and research is being done on ceramic replacement joints. Additional patents in the area of "open knee" surgery include U.S. Pat. Nos. 5,171,244 (Caspari et al 1992) and 5,358,525 (Fox et al 1994).
The second major type of approach to repairing knees and other joints is generally referred to as "arthroscopic" surgery. This approach is sometimes called "minimally invasive surgery," but that term is broader and not precise. "Arthroscopic" surgery involves cutting two or more small holes through the patient's skin, near the area to be worked on. A slender light source (usually a flexible fiber optic cable) coupled to a miniaturized lens for a video-type camera are inserted through one hole, so the surgeon can see what he (or she) is doing beneath the skin. One or more tissue manipulating instruments (such as a scalpel blade, a scissors-type cutting device with one or two movable blades, a gripping device such as forceps or a clamp, etc.) are inserted through a second and possibly additional holes. Various patents that disclose instruments or devices that can be used for arthroscopic knee repair or other types of similar surgery (such as laparoscopic surgery) include U.S. Pat. Nos. 4,203,444 (Bonnell 1980), 4,983,179 (Sjostrom 1991), 5,304,181 (Caspari et al 1994), and 5,322,505 (Krause et al, 1994), and numerous other patents as well.
In recent years, the boundary lines between open-knee surgery and minimally-invasive knee surgery have become blurred. For example, various patents issued to Caspari et al (including U.S. Pat. Nos. 5,171,244; 5,263,498; 5,336,266; and 5,395,376) relate to steel-type devices that may be several inches wide or long, which are inserted into the knee through incisions that may also be several inches long. Although this is not truly arthroscopic surgery, it can be called "minimally invasive" surgery, since any incisions that are made through the skin are kept to a minimum size, in view of the needs of the surgery. Accordingly, "minimally invasive surgery" is regarded herein as a much broader and less precise term, which includes both arthroscopic surgery, as defined above, and various other types of surgery in which any incisions through the skin are kept as small as possible. "Minimally invasive surgery" clearly excludes so-called "total knee replacement"; however, nearly any other type of skillful surgery on a knee might be regarded as "minimally invasive", under the broadest implications of the term.
Implantable Meniscus Devices PA1 Implantable or Injectable Polymers PA1 Implants that Promote Cellular Growth
The current invention relates solely to implantable devices that are securely anchored to a bone surface. As such, it does not relate to items of prior art involving surgical implantation of a "meniscus", which is a peripherally-anchored device that is sometimes implanted in a damaged knee to provide a form of cushion between the femur and tibia bones. Artificial meniscus devices are disclosed in various patents such as U.S. Pat. No. 5,344,459 (Swartz 1994), which discloses a flexible plastic membrane in the shape of a donut or double-donut, with compartments that can be filled with air, a liquid, or a semi-solid after the device has been inserted. To the best of the knowledge and belief of the Applicant (who is a surgeon, specializing in knee surgery), the device disclosed in Swartz's '459 patent is not commercially available, and is not being used by surgeons who perform knee surgery.
Another non-anchored implantable meniscus is disclosed in U.S. Pat. No. 4,344,193 (Kenny 1982), and a somewhat similar non-anchored "spacer" which assertedly can prevent unwanted motion of a kneecap in a damaged knee is described in U.S. Pat. No. 4,052,753 (Dedo 1977).
As mentioned above, these devices are not relevant herein, since the current invention relates to repairing or replacing damaged cartilage. The difficulties and challenges that arise in repairing or replacing cartilage, which requires that any implanted repair device must be permanently and securely anchored to an exposed bone surface, are substantially different from placing a movable device such as a meniscus or spacer inside a joint.
Several U.S. patents disclose various types of polymers or proteins that, assertedly, can be injected into a joint as a liquid or semi-liquid composition that subsequently harden into a solidified material.
For example, U.S. Pat. No. 5,556,429 (Felt 1996) discloses injection of a fluidized mixture of a biocompatible polymer (such as a silicone or polyurethane polymer) and a biocompatible "hydrogel" (a hydrophilic polymer, formed by steps such as using an agent such as ethylene dimethacrylate to cross-link a monomer containing a hydroxyalkyl acrylate or methacrylate), into a joint such as the knee, after one or more bone surfaces have been properly prepared. After injection, the polymer and hydrogel mixture can be set into solidified form by means such as ultraviolet radiation, which can be introduced into the subcutaneous area by a fiber optic device. Felt's '429 patent asserts that after the polymer-hydrogel mixture has set, it can be finished and sculpted by means such as using a retractable scalpel with an electrically heated tip that can reach boiling temperature to melt the surface of the polymeric material, thereby allowing it to be sculpted or otherwise modified by the spatula tip. After the heated tip is removed from the polymer surface, the melted surface material will cool again, and will solidify in its newly sculpted form.
That approach may offer promise, but it is not being used by surgeons, and it apparently suffers from several limitations and drawbacks. First, a surgeon's ability to ensure complete and thorough setting of a polymer-hydrogel mixture (especially those portions of the mixture that are directly next to a bone, and thus obscured from direct exposure to ultraviolet light) is limited and uncertain. Second, a surgeon has only limited ability to ensure that the polymerizing fluid, once it sets, becomes securely and permanently anchored to the bone surface.
Concerns over adhesion are highly important, for at least two reason. Most notably, the presence of a hydrogel mixed with the polymer will detract from the adhesive strength of the final polymer. A hydrogel necessarily has a high water content, and the water in the gel cannot and will not adhere to the bone; to put it in simple terms, a hydrogel is included in the mixture in order to make the final material slippery, rather than sticky. In addition, polymeric agents that have been selected for toughness, smoothness, and durability, but which also must provide a substantial amount of non-rigid, non-brittle cushioning in a manner comparable to cartilage, are not likely to also have the characteristics of an ideal adhesive.
Those important limitations, as well as various others, are addressed and overcome by the subject invention disclosed herein.
Additional prior art on surgically implantable polymers is contained in numerous published items; recent review articles include Peppas et al 1994, Hubbell 1995, Stokes 1995, Burg et al 1997, Lewis 1997, Kim and Mooney 1998, and Ambrosio et al 1998. Other discussions of biocompatible implantable materials are also available in various textbooks, such as Silver 1994.
A large amount of research has been carried out on various methods and devices for implanting chondrocyte cells (which generate cartilage, under proper conditions) into damaged knees and other joints. Published articles which discuss such efforts include Brittberg et al 1994, Chen et al 1997, Minas et al 1997, and Thornhill 1997.
Various U.S. patents that are relevant in this field include U.S. Pat. No. 4,919,667 (Richmond 1990), on a multi-layered implant with alternating layers of impermeable plastic to provide smooth sliding surfaces, and porous material to promote ingrowth of cells; U.S. Pat. No. 4,880,429 (Stone 1989), U.S. Pat. No. 5,007,934 (Stone et al 1991), and U.S. Pat. No. 5,306,311 (Stone et al 1994), all of which relate to porous matrices made of natural substances such as collagen, the protein that holds connective tissue together; U.S. Pat. No. 4,846,835 (Grande 1989), which describes techniques for growing chondrocyte cells in vitro, seeding the cells into a collagen matrix, and implanting the matrix and cells in the knee; U.S. Pat. No. 5,041,138 (Vacanti et al 1991), which describes synthetic but biodegradable polymers for use as a matrix material instead of collagen; U.S. Pat. No. 5,206,023 (Hunziker 1993), which discloses a multi-step process for cleaning a cartilage defect and then packing it with material that encourages chondrocyte cells to grow in the repair zone; and U.S. Pat. No. 5,769,899 (Schwartz et al 1998) which discloses a two-component implant which includes a slow-release drug delivery implant that delivers drugs or "repair factors" to a cell-growing implant.
Such efforts to use transplanted chondrocyte cells to regenerate cartilage in a damaged joint suffer from several limitations. Perhaps the most important limitation arises from the fact that under the current state of the art, chondrocyte cell transplants can only be used to repair cartilage defects that are about 1 square centimeter, or smaller, in size. Diligent efforts to work with larger areas have been tried, but the success rates in such efforts drop off sharply when the size of the cartilage defect increases; by the time a defect covers about 2 square centimeters or more, the success rate for chondrocyte-mediated repair is very low. Therefore, repair of a large defect in a cartilage surface of a knee normally requires a "total knee replacement." Accordingly, although chondrocyte transplants are useful for treating many types of sports injuries and other types of mechanical trauma or injury (such as automobile or bicycling accidents, falls, etc.), they are severely limited, and in most cases totally useless, for treating elderly patients, patients suffering from osteoarthritis, and various other types of patients with defects larger than about 1 to about 1.5 square centimeters.
In addition to that size limitation, collagen or other porous proteinaceous matrices disclosed in the patents by Stone, Hunziker, or Grande are not tough and durable, so it is difficult or impossible to anchor them to a bone surface that is subject to loading conditions.
It also should be recognized that repair methods involving transplanted chondrocyte cells under the prior art require long recovery times, compared to other approaches such as a "total knee replacement" using a mechanical joint. Typically, a patient receiving a chondrocyte cell transplant in a knee joint is prohibited from putting any weight on the knee for at least 6 weeks, and many patients are told to not put any weight on the knee for even longer periods, such as 12 weeks. Even after a patient can begin using the knee again, full recovery from chondrocyte cell transplant surgery typically requires numerous months. This type of slow and prolonged recovery period greatly increases the total costs of treatment and recovery (including, in many cases, lost work and lost wages). By contrast, a patient who has a "total knee replacement" (TKR, which involves sawing off and removing a damaged knee joint and replacing the joint with a mechanical device attached to the tibia and femur bones by steel pins) can usually begin to put weight back on the knee within a day or two after the surgery.
The very long recovery period required by chondrocyte cell transplants under the prior art also tends to limit candidate patients to relatively young people who were injured in a sporting event, auto accident, etc. Elderly patients, who are not as active and who will not have to live with a serious knee problem for another 40 years or more, are usually advised to get "total knee replacement" surgery instead.
In summary, chondrocyte cell transplantation is a relatively new technique. Although it holds good promise for some people (especially young people who have suffered an injury rather than a disease), under the current technology, it can only be used to repair cartilage defects that are about 1 square centimeter or smaller in size. Repair of larger defects in a cartilage surface normally requires a mechanical "total knee replacement" rather than a cell implantation procedure.
Accordingly, one object of this invention is to disclose improved methods and devices for replacing damaged cartilage in a knee, using arthroscopic methods, tools, and devices, in a way that eliminates the need for cutting open a knee to provide full exposure of the joint or the cartilage area that needs to be repaired.
Another object of this invention is to disclose a method of arthroscopic surgery on knees or other joints, which is capable of replacing an entire femoral condyle or tibial medial or lateral plateau with a hardened synthetic device, and which thereby overcomes and avoids the size limitation of other repair methods that can only repair a cartilage defect up to 1 square centimeter in size.
Another object of this invention is to disclose a method of arthroscopic surgery on knees or other joints, in which a device is implanted inside the joint, wherein the device provides an immediate and substantial improvement in the condition and operability of the joint, without requiring a delay of weeks or months before weight-bearing or other loads can again be placed on the repaired joint.
Another object of this invention is to disclose a flexible "scaffold" that can be rolled up or folded to allow it to be inserted into a joint through a minimally invasive incision, after a piece of damaged cartilage has been removed. Once the scaffold has been inserted into the joint, it can restored to its original shape, anchored to a bone surface, then filled with a polymer that will harden inside the scaffold, to create a polymeric replacement for damaged cartilage that can be implanted via an arthroscopic incision regardless of the size or surface area of the final implanted device.
Another object of this invention is to disclose a method of using a flexible scaffolding device which, using arthroscopic surgical tools, can be inserted into a diseased or damaged joint such as a knee, properly positioned over a bone surface from which the cartilage has been removed, anchored permanently to the bone surface, and then filled with a curable polymer.
These and other objects of the invention will become more apparent through the following summary, drawings, and description of the preferred embodiments.